From 34fb077ceed5166f4426daf21287d2ff4c0d65ca Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
Date: Thu, 2 Jul 2020 13:53:20 +0100
Subject: [PATCH] serial: 8250: bcm2835aux - defer if clock is zero

See: https://github.com/raspberrypi/linux/issues/3700

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
---
 drivers/tty/serial/8250/8250_bcm2835aux.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/tty/serial/8250/8250_bcm2835aux.c
+++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
@@ -180,6 +180,13 @@ static int bcm2835aux_serial_probe(struc
 	 */
 	up.port.uartclk = uartclk * 2;
 
+	/* The clock is only queried at probe time, which means we get one shot
+	 * at this. A zero clock is never going to work and is almost certainly
+	 * due to a parent not being ready, so prefer to defer.
+	 */
+	if (!up.port.uartclk)
+	    return -EPROBE_DEFER;
+
 	/* register the port */
 	ret = serial8250_register_8250_port(&up);
 	if (ret < 0) {
